That hissing sound you hear is the air being let out of Bruce Willis as he struggles mightily to reconnect with his once-vital action-comedy chops in the dim, unfunny “Once Upon a Time in Venice.”

It’s bad enough that Sergio Leone is inexplicably evoked by the title: there’s nothing epic, mythic, artful or entertaining about this tired private eye lark set in Los Angeles’ seaside enclave (not the Italian city), and it barely knows how to tell a story. A more appropriate storybook-themed title would have been, “Meanwhile, You Lose 90 Minutes.” As for Willis, there’s no happily ever after.

But what it draws out of director and co-writer Mark Cullen (who previously wrote “Cop Out,” also starring Willis) is comic laziness: retrograde point-and-laugh gags about linebacker-sized, motel-prowling male prostitutes in ill-fitting dresses and smeary lipstick, and a real estate agent Adam Goldberg plays called, repeatedly, “Lew the Jew.” (His last name is Jewison, as if that makes it … funnier?)

Willis’ character is a P.I. named Steve Ford, who runs a small agency with a young partner named John, played by Thomas Middleditch, who narrates because somebody’s always narrating in a private-eye movie, one assumes the thinking went. Steve has an ex (Famke Janssen) and a teenage daughter, drinks too much coffee, and lectures kids at the skate park about not making bad decisions in life — that would be of the avoid-hookers-and-blow variety, not the kind where you shouldn’t star in certain movies. Of course, Steve then turns around and sleeps with a sex-addicted young woman (Jessica Gomes) he’s been tasked with finding, which puts him in the crosshairs for a beating by her ripped-and-angry brothers.

After evading their clutches by skateboarding naked through the city — an un-edgy non-gag that goes on forever, and which Cullen might have had in a drawer since the ’70s streaking craze — Steve finds himself beholden to the pizza parlor employee named Tino (Adrian Martinez, “Office Christmas Party”) who shelters him. Tino wants Steve to get his car back from a fearsome local drug dealer named Spyder (Jason Momoa). Steve retrieves the automobile, but incurs the wrath of Spyder, who exacts revenge in the form of taking Steve’s terrier, Buddy.

This is apparently some kind of line-crosser for Steve, even though the movie doesn’t bother to introduce Buddy until well after the movie’s started, but if you’ve seen “John Wick,” the last word in don’t-mess-with-my-dog payback, the limp shenanigans that ensue will feel especially undeserving of the man’s-best-friend conceit.

As much as the movie has a screenplay (Cullen wrote it with his brother Robb), it’s of the one-thing-leads-to-another kind, none of which draws on what’s genuinely fun about detective movies or “After Hours”-style wild goose chases. But there are pitstops to depict mostly non-white subcultures — from the Latino gang Spyder runs to the aforementioned prostitutes to the black nightclub where Steve has to retrieve a briefcase full of coke — as criminal and/or laughable.

Venice doesn’t even come off as magically weird or enticing as a creative haven: a running gag about an underground artist-tagger who draws obscene paintings Banksy-style overnight on the side of an apartment building simply refuses to work.

In any given scene, Willis flirts with looking bored, distracted, or unsure of whether he’s supposed to be funny or tough. Considering how effortlessly his wiseass-badass persona once dominated movies, this development comes off as more disappointing than you’d think.

Middleditch, meanwhile, so good on “Silicon Valley,” just churns out more of the same hem-and-haw haplessness he’s known for, but at least his delivery is humorous even when the material doesn’t warrant it. And John Goodman, as Steve’s pal Dave, who’s getting a divorce and eventually joins in on the high jinks, might have just wandered onto the set and found himself with a role — such is the impact his character has on the proceedings.

A stroll along the Venice boardwalk is likely to elicit more laughs, and probably even thrills, than “Once Upon a Time in Venice.” How lazy is this movie? It makes a point of mocking the character of Spyder for spelling it with a “y,” then spells it with an “i” in the credits.

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